Can someone please explain to me how it happens that some cars have high torque (low rpm), but relatively low HP?

For example:
(1) RSX hp: 200, hp rpm: 7400, torque: 142, torque rpm: 6000
(2) Cavalier hp: 115, hp rpm: 5000, torque: 135, torque rpm: 3600

The torque is high on the cavalier, but it's hp is almost half, and both rpms are much lower. How does that work? And what is high-end or low-end torque?

Thanks in advance for any help.

 

most hondas torque power is flat all the way to redline...good for accelerating...
if u want a better understanding then u gotta look at a dyno sheet of both cars
everyone knows that domestics make gobs of torque due to bigger engines, but they have shorter redlines, they make peak power much lower then a typical honda...

timing is where u can change where ur peak power is...u adjust timing gears to make more power in the midrange for ur honda

my opinion based on daily driving

low = 1-3500
mid = 3500-5500
high = 5500- 8000

look at dyno sheets to compare thats my suggestion http://www.importreview.com
they have all types of cars dynoed

 

stroke and bore go into it a lot, cam lobes, flow paterns, timing there is a lot more that goes into it.

undersquare should yeild a higher torque down low. where an oversquare will yeild a higher hp. these are of course relative to each other, and considering all other things being equal. so if you had an engine that has 84mm bore and 88mm stroke (undersquare) you will yeild more torque than the same exact engine with a 88mm bore and a 84mm stroke (oversquare).

cam lobes, big fat overlapping cams have massive hp high up and no power down low, where mild cams give you better low end performance.

flow paterns, you can set up your flow so that it can breathe massive ammounts of air, which is good for high rpm, but down low this will hurt, because the air isn't traveling at a good velocity so that the air carries itself for lack of a better term, the air will have to be pushed out and pulled in by the engine, using power, whereas if the air can travel at a sufficient velocity, it can flow well on its own. it only makes sense that if the air passages are really small and designed for good velocity at low rpm then the higher rpm will be starved for air, since it is effectively choked, trying to flow more air than the passages allow.

all of these put together along with other things, will determine at what rpm and how strong the engine makes torque and HP. engines are all give and take, if you get something you have to sacrifice something else. there is no such thing as free power across the board (well, there is higher VE, but that is just better efficiency and through better efficiency better power across the board).

it is really confusing stuff, and it has been at least 5 or 6 years since I studdied this stuff, so if I am wrong on any of my points, please accept my humblest appologies

 

annother tidbit of info for you, torque and HP will be exactly the same at 5252 rpm, no matter the car, no matter the flow, no matter how high the hp is in compairison with the torque, or vice versa.

I don't remember what the formula is for calculating hp, but it is something about rpm and torque. I am sure the formula is somewhere out there on the internet, if you really care

edit, I was just checking for the formula myself (because I knew I would be wracking my brain all day if I didn't..) and found this nifty little site http://www.datsuns.com/torquehp.htm go about halfway down the page and it shows the calculation for hp and torque.

HP = (torque*rpm)/5252

to figure out what 5252 comes from you have to read the page


[Modified by samagon, 4:04 PM 10/3/2001]

 

Yeah, I've read about that formula before. There's this guy I know who was talking big about how his cav is so powerful and etc etc... I should just make him race me, even tho my teg is a slow auto.

Thanks a lot for the info guys.

 

This is where something like VTEC or VVTi comes into play. It's much easier to make an engine that does one of the other well, but not both.

For example, a typical LT1 engine out of a '93-'97 f-body has a shitload of low end torque and a nice flat torque curve. My buddy's '97 Formula makes peak torque at 2000 rpm, at 301 rwtq. The problem is that engines like this tend to run out of steam at around 5000 rpm or so.

The opposite of this is my Cobra, the peak torque value is much lower, but at a much higher rpm- 272 rwtq at 4800 rpm. My engine makes good power up until 7000 rpm, but down low it sucks (anything under 3500 is dog slow). Incidentally I do make more hp than my friend's car, but he's got me beat in the torque department.

An engine with variable timing can have it both ways, a nice flat torque curve but also a useful upper rpm range. It's pretty cool, really.

 

this is exactly true.

hey milano, annother thing you should think about, because HP and torque is only a small part of the of the speed equasion, gearing, weight and drag make up the rest of it.

there are some cars that have massive hp, tque ratings, but they weigh a ton and have really tall gears, or something that has a hp of like 100 with the right gearing, or weight could easily blow the doors off of any car.

that is why a bike with only 100hp can do so well against a lambroghini or viper for instance, they have 4x as much power, but they weight a lot more and the gearing is not as short as the bike.

these all factor in.

 

Well, here's a simple way of thinking about it. The best torque curves are the ones that are flat, from 0-redline. This is impossible, mind you, but an engine that creates as flat of a torque curve from 0-redline are the best. However, most engines fall under 2 categories:

1. A torque curve that is pretty low in peak value, but pretty flat until redline. This is the torque curve of most import sport compacts. Those with variable timing (VTEC, etc) will be the ones whose torque curves stay flat until redline, but even non-variable timing engines will do a pretty good job of maintaining power till redline (albeight, a lower redline). This kind of engine has the potential to produce a lot of HP, simply because HP = rpm x torque / 5255. If you look at that equation, if you can produce say 120 lb-ft of torque at 5,000 rpm, that's
114hp, but if you can produce it at 10,000rpm, that's 228hp. Big difference, eh? That's why low torque, high-rpm engines can produce lots of hp. The way you take advantage of this hp is by gearing (and weight reduction, since low torque engines will produce very little torque near idle speed, and you can't always be downshifting).

2. The torque curve is very meaty down low (below 4k rpms) but start to drop off fast after that. This is the torque curve of many domestics (a great example is the Mustang GT). Although it makes a lot of power down low, it runs out of breath up top. That's why peak hp isn't as great as you would expect, considering the peak torque value. However, they produce enough torque at a decent rpm, to make lots of hp as well (more than most imports as well, which is why imports need to weigh less to compensate)

The best engine would produce lots of torque down low, and lots of hp up top (which is reflective of a flat torque curve.) HTH - gotta run to go study now

 

So the best shift points for a certain car would be where your engine begins to lose torque?

For example:


Where would be the best shift point for this car? By the way, can anyone modify my engine to look like this and still pass smog/emissions?


[Modified by 2001 Integra GSR, 4:23 PM 10/3/2001]

 

what is up with that dyno chart? that dip is crazy, it almost looks like the wheels slipped on the dyno at 5k and then got grip again at about 6k.

can anyone else explain how that would look like that? aside from maybe vtec engaging too early..

 

Thank you all very much. This has been really helpful.

 

it is standard to see a significant torque dip before the short runners open up....but i dunno, thats a pretty huge jump in the curve. Ive seen that before, but on much more built blocks


[Modified by D-SPEED, 2:57 AM 10/4/2001]

 

The dip is so obvious because of the scaling. Look at the scaling.

Dustin

 

IN one of my magazines it shows the formula for calculating your ideal shift points, i'm sure the info is out there, try Tuan at sho.org, he might remember the formula

 

You have to know the gear ratios to calculate optimum shift points.

The idea is, shift to the next gear when there is more torque available at the wheels IN THE NEXT gear at the destination RPM than in the current gear at the current RPM. If there is no point when there is more effective torque in the next gear, shift as high as possible.

Most hondas have almost entirely flat torque curves (especially those with VTEC). With our motors, we almost always want to shift as high as possible... because you always loose wheel torque with a shift.

Dustin

 

Each shift, your changing the gears, which essentially are torque multipliers......overall HP never changes...but the driving force, the torque does.....as you move up in gears, your trading torque for speed......since HP is a product of torque and speed, and the gears are mutlipliers, power doesnt change, torque does...

 

youd have to spend A LOT of time to determine what RPM you'll be in in the next gear when you shift, taking into accountability, shift quickness, shift RPM, up hil, downhill, and what not. But i know there is a formula it's just taucked away in one of my thousands of magazines.